1. Field of the Invention
The present invention relates to patch antennas, and more particularly, to tunable patch antennas with a patch and switches to one or more tuning strips which when coupled to the patch by the switches adjust the antenna resonant frequency.
2. Description of Related Art
Many applications require small, light weight, efficient conformal antennas. Traditionally microstrip patch antennas have been a preferred type for many applications. These applications tend to be only over a narrow frequency band, since microstrip patch antennas typically are efficient only in a narrow frequency band. Otherwise, the advantages of these antennas of being mountable in a small space, of having high efficiency and of being capable of being constructed in a rugged form, have made them the antennas of choice in many applications.
Satellite communication (Satcom) systems and other similar communications systems require relatively broadband antennas. Typical military broadband applications include long range communication links for smart weapon targeting and real time mission planning and reporting. A variety of antenna designs, such as crossed slots, spirals, cavity-backed turnstiles, and dipole/monopole hybrids have been used for similar applications over at least the last 15 years. However, most of these antennas require large installation footprints, typically for UHF antennas, a square which is two to three feet on a side. When used on aircraft, these antennas intrude into the aircraft by as much as 12 inches and can-protrude into the airstream as much as 14 inches. For airborne Satcom applications, antennas of this size are unacceptably large, especially on smaller aircraft, and difficult to hide on larger aircraft, where it is undesirable to advertise the presence of a UHF Satcom capability. Therefore, there has been a need for small highly efficient broadband or frequency-reconfigurable narrowband antennas, not just in these applications, but in many other new and different commercial applications. For example, one possible application is a multiband multimode mobile phone that operates in the GSM 900 MHz, PCS 1900 MHz, and DES 1800 MHz bands, although not simultaneously.
A patch antenna is composed of a segmented patch and MEMS switches which are built on a substrate. The patch segments of the segmented patch can be electrically connected to each other by the MEMS switches to form a contiguous patch and optional tuning strips and to permit or block the flow of RF currents between the contiguous patch and the optional tuning strips. When RF is connected between the tuning strips and the contiguous patch, the tuning strips increase the effective length of the contiguous patch and lower the antenna""s resonant frequency, thereby allowing the antenna to be frequency tuned electrically over a relatively broadband of frequencies. When the tuning strips are connected to the patch in other than a symmetrical pattern, the antenna pattern of the antenna can be changed. In another aspect of the invention, fine tuning in accordance with desired frequency, input impedance and/or polarization can be achieved by selectively connecting patch segments in reconfigurable patterns using switches. A planar inverted F antenna (PIFA) is also provided with one or more tuning strips spaced from the lid of the PIFA and with switches to connect or block RF between the lid of the PIFA and the tuning strips.